martial arts fighter, was friends with boston bomber tamerlan tsarnaev. they even trained in the same gym. >> they used to hang out. not hang out, he knew him because he was an mma fighter and the other guy was a boxer. >> reporter: the fbi had been talking to todashev for weeks after they discovered he called tsarnaev days before the bombing. suddenly he lunged at the fbi with a knife and was shot and killed. todashev was about to sign a confession in connection with a triple homicide in the boston area. the three men had their throats slit, marijuana and cash sprinkled over their bodies. since the bollings, tamerlan and his younger brother dzhokhar have emerged as suspects in the killing. there's no evidence so far tying todashev to the bombings.